Giant Knotweed

Genus: Polygonum

Species: sachalinense

Description: Hollow upright, bamboo-like stems grow to 1-5 meters (3-16 ft) tall. Has large, smooth-edged leaves and small white or greenish flowers that bloom from July to August and grow in dense clusters.

How it spreads: High water and floods sweep plants into rivers and creeks, them fragment and disperse plant parts. Root and stem pieces, as small as 1 cm (1/2 inch) can form new plant colonies.

What it threatens: Grows faster than most other plant species (including natives) and quickly outgrows and suppresses or kills them.

More information: Nature Conservancy website

Disclaimer - Clean Water Services does not endorse or recommend specific herbicides for use in controlling these species. To protect water quality, always follow herbicide label directions and obey application laws when using any herbicide.